In image reading apparatuses included in copiers, scanners, and multifunction apparatuses having a copy function and a scanning function, auto document feeders (“ADF”) are known that feed documents from an input tray through a feed path to an output tray. In addition, in order to read a document printed on a first surface and a second surface, document feeders that feed a document for double-side reading by reversing its leading end and trailing end are known.
FIG. 33 shows a feed path in an existing document feeder capable of double-side reading. As shown in the figure, a document P is placed on an input tray 100 with a first surface (a first page) facing upward. This document P is fed to a feed path 102 by a pickup roller 101. In the feed path 102, the document P is fed by feed rollers 103 provided as appropriate, and the first surface of the document P is read by an image reading device, such as CCD or CIS, when it passes a reading position X. When a sensor detects a trailing end of the document P, of which the first surface has been read, ejection rollers 104 are stopped with the trailing end of the document P nipped.
Then, as shown in FIG. 34, as the ejection rollers 104 are rotated backward, the document P is fed to a switchback path 105. The document P goes from the switchback path 105 toward an upstream side of the reading position X of the feed path 102. As a result, the leading end and the trailing end of the document P are reversed, and the document P is inverted. Then, the document P is fed by the feed rollers 103, and the second surface of the document P is read by the image reading device when it passes the reading position X. When a sensor detects the trailing end of the document P, of which the second surface now has been read, the ejection rollers 104 are stopped again with the trailing end of the document P nipped, and then the document P is fed back to the switchback path 105. When the document P enters the feed path 102 again from the switchback path 105, its leading end and trailing end are reversed again, that is, the first surface faces the reading position X, and the document P is again inverted. The document P then is fed on the feed path 102 and ejected to an output tray 106 with its first surface facing downward. Thus, the first and second surfaces of the document P are read, and the document P is ejected to the output tray 106 in the same sequence as the original documents P, in the original order, placed on the input tray 100.
The pickup roller 101, the feed rollers 103, and the sheet ejection rollers 104 are rotated through power transmission from a motor. The pickup roller 101 and the feed rollers 103 are always rotated in one direction, i.e., in a direction to feed the document P from the upstream side of the feed path 102 to the downstream side thereof. The sheet ejection rollers 104 are rotated in both forward and reverse directions to feed the document P back along the switchback path 105. For example, as shown in FIG. 34, when the document P is nipped between the feed rollers 103 and the sheet ejection rollers 104, a sheet feeding direction of the feed rollers 103 should match a sheet feeding direction of the sheet ejection rollers 104. In addition, when the document P is nipped between the feed rollers 103 disposed directly downstream of the reading position X and between the sheet ejection rollers 104, the sheet feeding direction of the feed rollers 103 should match the sheet feeding direction of the sheet ejection rollers 104. Thus, as an example, when separate motors are provided for driving the feed roller 103 and the sheet ejection rollers 104, the feed rollers 103 may always be rotated in one direction, and the sheet ejection roller 104 rotational direction must be changed at a predetermined timing.